(1) Field of the Invention
The present invention relates to an easily-openable vessel closure. More particularly, the present invention relates to an easily-openable vessel closure having excellent shock resistance and an opening shape suitable for drinking a liquid content.
(2) Description of the Prior Art
A vessel closure comprising a can end member having a preformed opening and an easily-tearable opening tab arranged on the outer side of the can end member to cover said opening and adhere closely to the peripheral portion of the can end member contiguous to the opening is known as an easily-openable vessel closure. Bonding of the opening tab to the can end member is accomplished by using a pressure-sensitive adhesive or by heat sealing with a hot-adhesive resin. In each case, if insufficient adhesion or peeling is caused between the opening tab and the peripheral portion contiguous to the opening, a serious problem of insufficient sealing due to leakage arises.
Various proposals have been made to protect the cut edge of the opening and improve the pressure-resistant bonding between the opening tab and the peripheral portion of the can end member contiguous to the opening in easily-openable vessel closures of this type. However, trials have hardly been made to protect the bonded portion between the opening tab and the peripheral portion contiguous to the opening from shocks of falling or the like